Valve sizes- help me understand : V-Twin Forum: Harley Davidson Forums

bowtech40 · 10-23-2009, 05:52 PM

Was looking at different sites today to kill some time, and noticed the different valve sizes on the high dollar heads offered by some of the better know builders. Zippers has a 2" intake and a 1.630 ex, T-man makes his stage 4 with a 2.020 amd a 1.615 etc. Am I correct to say that the bigger intake is more for top end power, or does the rest of the porting come into play to? Are heads like this only for big inch motors, or can they be used say on a 103" or smaller with good results? Just curious, as I know cylinder fill is important, but so is velocity.

claydbal · 10-23-2009, 07:42 PM

the holy grail! good question! i have been asking the same forever. got the best explanation from hillside and bean. there are others, but these guys explained it so i could understand.

baggersport · 10-23-2009, 07:55 PM

Quote:

Originally Posted by claydbal

the holy grail! good question! i have been asking the same forever. got the best explanation from hillside and bean. there are others, but these guys explained it so i could understand.

I got more better stuff too Dennis....when you're ready......

.

claydbal · 10-23-2009, 07:58 PM

give me time man, im still trying to absorb what you and scott told me. im slow ya know. LOL

baggersport · 10-23-2009, 08:15 PM

Quote:

Originally Posted by claydbal

give me time man, im still trying to absorb what you and scott told me. im slow ya know. LOL

...ahhh, yes......I 'member. It will help ya tie more of it togethah...

...we'll get you in on a conference call....feed you info till you squeeeel like a pig.....LOL

.

Hillside · 10-23-2009, 08:17 PM

Different applications, different valve sizes, but you do get limited to only so large, when needed, as valve to valve at TDC can become an issue, with some of the bigger cams. Shape of the valve is also important.

Scott

wfolarry · 10-23-2009, 08:59 PM

Food for thought:
I built 2 124's for twin brothers. Their bikes were like them - identical twins. The only difference was the heads. One had a set of Zipper's CNC heads that I tweaked & the other had B2 heads. Off the line the Zippy bike was quicker. After about 1/2 way down the B2 head started coming on. At the finish line the B2 head was way out in front. The interesting thing about it was on the dyno they both made 170 HP. Think about it.

Okla.Dave · 10-23-2009, 10:16 PM

Quote:

Originally Posted by wfolarry

Food for thought:
I built 2 124's for twin brothers. Their bikes were like them - identical twins. The only difference was the heads. One had a set of Zipper's CNC heads that I tweaked & the other had B2 heads. Off the line the Zippy bike was quicker. After about 1/2 way down the B2 head started coming on. At the finish line the B2 head was way out in front. The interesting thing about it was on the dyno they both made 170 HP. Think about it.

Would this be due to one making it’s H.P. and torque to early.
The other making it’s H.P. and torque later.
The later tq. and h.p. used its gears at first and later used tq. and h.p. to move the bike quicker?

Does that sound right?

qtrracer · 10-24-2009, 12:27 AM

Sounds like the B2 in that application is faster to the finish. I will leave all the technical jargon to those who can speak and understand it, I only understand winning and losing.

towboattrash34 · 10-24-2009, 01:28 AM

Then look at R&R's with raised ports and Baisley's Hybrid heads they also have a raised ports.... if you go too big for your cam you kill velocity then you have to work the ports.... you can have too much velocity also..... you said something about T-Man's 4 heads.... compare the flow chart to his 3 heads and tell us what you see....

here is his flow charts if someone care to explain them.....
stage 2

stage 3

stage 4

towboattrash34 · 10-24-2009, 01:35 AM

if you look at stage 3 and 4 you see with a bigger intake it more flow but killed some of the exhaust flow.... both have same exhaust valve... now what would need to be done to bring up the exhaust flow???? or would you??? maby Scott or wfolarry or Bean could tell us a story ???? which would be a better head 3 or 4 ???

strokerjlk · 10-24-2009, 09:03 AM

Quote:

Originally Posted by towboattrash34

if you look at stage 3 and 4 you see with a bigger intake it more flow but killed some of the exhaust flow.... both have same exhaust valve... now what would need to be done to bring up the exhaust flow???? or would you??? maby Scott or wfolarry or Bean could tell us a story ???? which would be a better head 3 or 4 ???

look at the cfm numbers on the left of the chart. It didnt kill the exhaust flow. just diff scale numbers. looks like ex stayed about the same. while intake increased with the increase in valve size.

claydbal · 10-24-2009, 09:54 AM

looks like ya need a biggass cam to work well.

KingofCubes · 10-24-2009, 10:19 AM

Quote:

Originally Posted by bowtech40

Was looking at different sites today to kill some time, and noticed the different valve sizes on the high dollar heads offered by some of the better know builders. Zippers has a 2" intake and a 1.630 ex, T-man makes his stage 4 with a 2.020 amd a 1.615 etc. Am I correct to say that the bigger intake is more for top end power, or does the rest of the porting come into play to? Are heads like this only for big inch motors, or can they be used say on a 103" or smaller with good results? Just curious, as I know cylinder fill is important, but so is velocity.

Right as far as my experience. The better heads have correct size valves for the application, the best cfm matched with velocity. This has been hashed over many times on this and other boards. Quick revving seems to come from the right blend of flow and air speed. The R&R stage 5 heads for instance will flow 295 cfm with a 1.94" intake valve at 28 inches of depression and show between 650 and 670 feet per second at 150 inches of depression throughout most of the lift range. These heads are the best choice for larger engines but not as early torque as the smaller port stage 4's with a 1.9" valve.

Knighty-Knight · 10-24-2009, 10:55 AM

Quote:

Originally Posted by wfolarry

Food for thought:
I built 2 124's for twin brothers. Their bikes were like them - identical twins. The only difference was the heads. One had a set of Zipper's CNC heads that I tweaked & the other had B2 heads. Off the line the Zippy bike was quicker. After about 1/2 way down the B2 head started coming on. At the finish line the B2 head was way out in front. The interesting thing about it was on the dyno they both made 170 HP. Think about it.

The above post answers a lot of questions if you read through it.

It also raises questions though:
Both bikes were twins, but should they have been?
Wouldn't both bikes benefit from different gearing given the different manifestations of power?

I think it also goes to show that peak numbers mean diddly squat.